Thesis (MScAgric)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Guayule (Parthenium argentatum Gray) is a semi-desert plant with the potential to become an
established crop on arid land in South Africa. The plant produces latex, which can be processed
into rubber that is useful in application where disease transmission needs to be limited, such as
for surgical gloves and condoms. The poor germination and natural dormancy characteristics of
the embryo and the seed coats of guayule seed, motivated germination experiments.
Germination of seed treated with solutions of gibberellic acid, smoke water and smoke watergibberellic
acid was determined. Furthermore, combinations of gibberellic acid, smoke water
and sodium hypochlorite treatment solutions were applied to seed to determine the germination
responses. Vegetative propagation of guayule by means of cuttings was also investigated to
determine the rooting responses of cuttings with treatment solutions of indole butyric acid,
naphthalene acetamide and naphthalene acetic acid. Rooting percentage, root length and root
weight was determined for each treatment. Dryland field trial plantings were established at
different areas in South Africa to determine the growth potential and biomass production of
guayule cultivars under different environmental conditions. Stand count, height, canopy
diameter and stem diameter was determined for the different cultivars and areas. Lastly, latex
production of guayule cultivars established in trial plots at Elsenburg, Oudtshoorn and Graaff-
Reinet was determined after one year of growth.
Treatment solutions of an aqueous smoke extract (commonly referred to as smoke water) and
gibberellic acid were evaluated to determine their effectiveness in stimulating germination of
four guayule seed lines (AZlOl, AZ-3, N565 and 11591). The split-plot analyses of variance
showed no significant interaction between cultivar and treatment factors (P = 0.71), but when the
day factor was included interaction was highly significant (P < 0.0001). The applied treatment
thus had an effect on the time required for the germination response. Investigations into
optimum germination responses indicated that smoke water-gibberellic acid required the shortest
number of days (6.3 days) for optimum germination to occur with cultivar AZ-3. Furthermore,
gibberellic acid treatment resulted in the greatest germination with the four cultivars 11591, AZ-
3, AZI0l and N565, at 93.78%, 93.35%, 94.41% and 99.42% respectively. These results show that guayule seed can be stimulated to germinate by treatment with gibberellic acid and smoke
water solutions.
Specific concentrations of treatment solutions of gibberellic acid, smoke water and sodium
hypochlorite, and combinations thereof were used to evaluate the germination response of
guayule seed cultivar AZ-2. Combinations of treatment solutions did not result in significantly
increased seed germination responses. Single treatment solutions of gibberellic acid and smoke
water did not significantly enhance germination, but sodium hypochlorite however, significantly
(p <0.0001) suppressed germination at the 1% Cl and 2% Cl concentrations with about 5% and
10% respectively when compared to the control. Therefore, the applied seed treatments did not
effectively increase the germination of guayule cultivar AZ-2 seed.
Specific concentrations of indole butyric acid, naphthalene acetamide and naphthalene acetic
acid treatment solutions were applied to guayule cuttings of cultivar AZ-3 and rooting response
was determined for rooting percentage, root length and root weight. Naphthalene acetic acid
treatment rooted the highest percentage of cuttings (52.38%) at a concentration of 60 mgll.
Indole butyric acid treatment produced the longest roots (147.83 mm) at a concentration of 120
mg/l. Naphthalene acetamide obtained the heaviest roots (1.8 g) at a concentration of 120 mgll.
Treatment solutions of indole butyric acid, naphthalene acetamide and naphthalene acetic acid
indicated specific concentrations for optimum effect to improve root formation (by 30%), root
length (by 50 mm) and root weight (by 1.5 g) when compared to the controls.
Guayule trial plots of IOx10 m, rows 1 m apart and 30 cm between plants, and each cultivar (10
plants per unit) placed at random and replicated 6 times, were established in different areas under
different environmental conditions in South Africa. Plantings were evaluated as a dryland
practice, though irrigation was supplied only for establishment. Growth (stand count, height,
canopy diameter, stem diameter) and biomass (wet and dry weight) were recorded for (1) oneyear
old plantings established in April 2001 at Elsenburg, Graaff-Reinet and Oudtshoorn, and (2)
six-month old plantings established in October 2001 at Bethulie, Glen and Upington. Analysis
of variance was done to determine mean growth and biomass for the different areas and cultivars.
(1) There were significant interactions between the factors area and cultivar for stand count and height, while canopy diameter and stem diameter differences were significant only within
factors. The greatest growth potential was produced by cultivars AZ-2 and AZ-3, and
Oudtshoorn was the best area for growth potential and biomass production. (2) Interaction
between area and cultivar was significant for plant height, but were not significant for stand
count, canopy diameter and stem diameter. Cultivars produced similar results for biomass
production, but were significantly different in the different areas of Bethulie, Glen and Upington.
Growth potential and biomass production of guayule was influenced by the availability of water
during the growth of the plant.
Latex production of guayule cultivars (AZ-2, AZ-3, N565, 11591) established in trial plots at
different areas (Elsenburg, Oudtshoorn, Graaff-Reinet) in South Africa was investigated. Branch
samples of one-year old plantings were harvested in April 2002, dipped in 1% ascorbate, sealed
in plastic bags and chilled during airfreight to the United States Department of Agriculture
(USDA) - Agricultural Research Service (ARS) in Albany CA. Latex extraction and
quantification was done and mean latex production and comparisons of latex production for the
cultivars in each area were determined. The evaluation of latex production show generally
similar results in the different areas. Cultivars generally do not differ significantly from each
other in the amount of latex produced in each area. Environmental stress factors on latex
production occur in especially Oudtshoorn and Graaff-Reinet where the temperatures are above
25°C and below 1DoC. Since guayule is a slow growing shrub, latex accumulation is also slow
and takes 4-6 years to reach economic harvesting potential. Production results are therefore
preliminary and require further evaluation after each year of growth to present a complete view
of guayule latex production over time.
Propagation investigations were successful in identifying techniques to germinate guayule seed
and promote rooting of cuttings with specialized treatment solutions. Field establishment of
guayule under South African environmental conditions has identified suitable areas and indicated
cultivar performances in these areas. Evaluation of the latex production of field plantings has
demonstrated the potential of guayule in these areas. Currently the path to guayule development
is paved with a network of research activities that is strengthened through cooperation between research institutions and private sector companies that bridge the gap between academic research
and market exhibition. / AFRIKAANSE OPSOMMING: geen opsomming
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52829 |
| Date | January 2002 |
| Creators | Bekaardt, Claude R. (Claude Ron) |
| Contributors | Pieterse, P. J., Stellenbosch University. Faculty of AgriSciences. Dept. of Agronomy. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 76 p. : ill. |
| Rights | Stellenbosch University |
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